During 1998 we have continued our investigations of the motor portion of myosin, subfragment 1 (S1), and have extended our studies to microtubule-based biomotors as well. Studies of skeletal myosin S1 have been extended to attempt to observe changes induced by various nucleotide and nucleotide analogs at high-Q and to model these results. In addition, we have initiated an investigation of changes in smooth muscle S1. Here it is believed that the kinetic intermediates are different and have a different structure than found for skeletal muscle S1. Preliminary results with smooth muscle S1, indicate that there are changes in structure between no nucleotide, MgADP addition and MgAlF4 addition. We also studied the solution structures of two microtubule-based motors: ncd and kinesin. We found that the scattering of ncd can be well modeled by the recently determined crystal structure, but that the kinesin structure cannot be well fit by a model based on the crystal structure of a kinesin construct (Stone et al., 1998). These results have implications for the mechanism of binding of kinesin to microtubules and possibly the mechanism of cellular movement.